1. Field Of The Invention
This invention relates generally to electromagnetic transducers for converting electrical signals to mechanical vibrations, and more particularly relates to a vibrator for operating at very low frequencies and applying sufficient power to a sounding board structure for enhancing the simulated realism of attending a live, musical or other audible event.
2. Description Of The Related Art
The experience of live music and other audible events includes not only the sensation of sound as sensed by human ears, but additionally includes the sensation of low frequency vibrations through portions or all of the human body. Consequently, reproduction of a faithful simulation of an audible experience includes not only reproduction of the sound through conventional sound transducers, such as speakers, but additionally includes reproduction of the low frequency vibrations by imparting such vibrations to a sounding board structure, such as a floor or wall of a room, or to articles, such as furniture within the room, so the sensation of physical motion at low frequencies may be perceived by the listeners.
Digital audio and high fidelity film and video monitor soundtracks are capable of recording these low frequency signals. However, modern bass speaker systems are expensive if they are capable of reproducing those sub-bass and sub-audio frequencies which are generated in live performances, movie sound tracks, and events. Practical bass speaker systems are designed to faithfully reproduce sound within an operating range of frequencies, but this range does not extend sufficiently low to also reproduce those frequencies which are the subject of this invention.
Prior art workers have proposed designs for vibratory transducers capable of operating in a low frequency operating range. Vibrators proposed for these purposes include those shown in U.S. Pat. Nos. 5,424,592; 3,178,512; 4,914,750; 4,788,968; and 4,675,947. These prior designs, however, suffer from one or more disadvantageous characteristics. One problem is that they exhibit an insufficient frequency response at the very lowest frequencies in the range below 30 Hz. Another major problem arises because such devices include mechanical springs which are required to both resonate a reciprocating mass and to hold the reciprocating mass in place within the device.
For example, U.S. Pat. No. 5,424,592 utilizes planar springs. However, planar springs inherently have a limited range of translation because of their structure. Beyond their limited range, their spring constant K increases non-linearly. Consequently, they have a narrow range of permissible deflection and therefore permit insufficient maximum amplitudes of oscillation of the reciprocating mass to which they are attached.
Still other vibrators, such as that shown in U.S. Pat. No. 4,675,907, utilize an elastomeric material as a spring, but this too has a very narrow band of permissible translation. Although coil springs might be used, these would greatly increase the length of the vibrator along its axis of reciprocation. Furthermore, all mechanical springs suffer from fatigue and heating and resulting power loss when subjected to large amplitudes of oscillation.
Finally, the prior art vibrators which have previously been proposed tend to utilize relatively complicated structures which are therefore expensive to manufacture and expensive to assemble.
It is therefore an object of the present invention to provide a mechanical vibrator which utilizes very simple structures which are easily assembled and which do not require a mechanical spring, and yet provide a strong centering spring force by a spring structure which is not subject to fatigue.
It is a further object and feature of this invention to provide a vibrator structure which has a very low ratio of spring constant to reciprocating mass, and therefore can exhibit a large amplitude, low frequency response, while, at the same time, permitting large translations, a large spring constant and large mass. The larger these latter three parameters are, the more energy storage in the oscillating, mechanical system, and therefore the more force and power applied to an attached sounding board structure where the audio experience is being reproduced.